Study On The Transfer Path Analysis Methods Theory And Its Practice In Lowering A Car Noise

Customers are more and more strict in automobile NVH performance, NVH performance has become one of the main indexes of the competitiveness ability of products. Automobile manufacturers have strengthened enforcement to improve automobile NVH performance. At present, for most of the domestic automobile manufacturers, during the process of developing NVH performance of a automobile, the rectification workload of NVH performance after physical prototype is made is more 70% than that during the whole NVH development process. So improving the efficiency and quality of the later rectification has important significance for a automobile NVH performance. Among the researches in NVH field, there are much more work have been done which in view of CAE analysis for performance and the real vehicle test, but less work have been done which in view of later NVH rectification during research and development process. Transfer path analysis (TPA) methods are effective tools to find the vibration and/or noise source. Some TPA methods have been proposed and applied, such as conventional TPA (CTPA), operational TPA (OTPA). These methods have advantages and disadvantages, some ones have high accuracy but low efficiency; some ones have the contrary conditions. In this paper, based on the principle of theoretical research to solve practical engineering problems, in view of later NVH rectification during a car research and development process, relying on the special fund for strategic emerging industry from Guangdong Province Development and Reform Commission, the theoretical research study about TPA methods were done, and its achievement was applied to solve NVH problems in a prototype car which interior noise exceed target.(1) CTPA has high accuracy, its result is often looked as benchmarking to other TPA methods, and its theory is the foundation of other TPA methods, taking a target car for object, the basic theory and application of CTPA method were studied, including the calculation and testing method of frequency response functions (FRFs), loads calculation method, transfer path contributions (TPCs) calculation method. Using CTPA method, analyzed the noise transfer paths in a prototype car which interior noise exceed target, found out the paths which contribution amount is larger to interior noise. The work in this chapter laid a foundation for theoretical research and practical application in the subsequent chapters.(2) OTPA method has a high efficiency, but a low precision.Use several ways to improve the OTPA method: ① Processing the collected signals using wavelet de-noising technology, this way effectively decreases the noise contamination in signals; ②removing the smaller singular values generated in singular value decomposition, retaining only the optimal singular values, so that the accuracy is further improved; ③ Dividing the calculated frequency into some bands, only one FRF in each band is calculated. The other FRFs are predicted using neural fuzzy logic algorithm. A user scenario was given that shows the application process of the improved OTPA method. Taking the test results in chapter 2 for benchmark, compared the results abtained by using the improve OTPA method and that ones abtained by using existing OTPA method with the benchmark, the comparison show that the improved method precision had beed improved.(3) To enrich theory of transfer path analysis methods, based on the study on the inverse sub-structuring technique, the inverse sub-structuring transfer path analysis (ITPA) was proposed. By the ITPA method, the dynamic stiffness of mounts of power train are calculated using the FRFs of the system and the sub-structure. And the loads are calculated based on the dynamic stiffness and the vibration parameters on both sides of mounts. Then the TPCs are calculated. During the calculation process, the noise contamination of signals is decreased using wavelet de-noising technology effectively. A user scenario was given that shows the application process of the ITPA method. Comparing the results in this user scenario with the benchmark in chapter 2, the determination coefficients was satisfactory.(4) The TPA theory was applied to solve the NVH problems in an automobile. The transfer paths and its contributions to the interior noise of a test car whose interior noise exceeds the limit were found out using the improved OTPA method and the proposed ITPA method. Combined with spectrum analysis technology and finite element analysis technology, the rectfication measures for the NVH problems was established. After conducting 3 rounds of rectification, the noise problem was solved. Based on the success of practice,using system engineering theory, a solving process of automobile NVH problem based on TPA method was summarized.In order to improve the efficiency and quality of later rectification in a car research and development process, this dissertation made some theory researches on TPA methods, and made verification of the the rationality and validity of the researches by engineering application. The theoretical study enriches the TPA theory and application research has great reference significance in engineering.